
class Users(list):
	def __init__(self):
		list.__init__(self)
		self.usernameUsage = set()

	def append(self, user):
		self.usernameUsage.add(user.name)
		list.append(self, user)

	def remove(self, user):
		self.usernameUsage.remove(user.name)
		list.remove(self, user)
	
	def __contains__(self, x):
		return x in self.usernameUsage

